CSS的display属性list-item的list-style-type显示不出来的问题解决

<!--以下是XML文档-->
<?xml version="1.0" encoding="GB2312"?>
<?xml-stylesheet type="text/css" href="student.css"?>
<!DOCTYPE student[
<!ELEMENT student (stu)*>
<!ELEMENT stu (name,sex,height)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT sex (#PCDATA)>
<!ELEMENT height (#PCDATA)>
]>

<student>
<stu ID="a110">
<name>A</name>
<sex>male</sex>
<height>175</height>
</stu>
<stu ID="a111">
<name>B</name>
<sex>male</sex>
<height>172</height>
</stu>
</student>

/*以下是CSS文档*/
student
{
display:list-item;
list-style-type:square;
font-size:24pt;
}

<?xml version="1.0" encoding="GB2312"?>
<?xml-stylesheet type="text/css" href="student.css"?>
<!DOCTYPE student[
<!ELEMENT student (stu)*>
<!ELEMENT stu (name,sex,height)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT sex (#PCDATA)>
<!ELEMENT height (#PCDATA)>
<style>
student
{
display:list-item;
list-style-type:square;
font-size:24pt;
}
</style>
<student>
<!--<stu ID="a110">
<name>A</name>
<sex>male</sex>
<height>175</height>
</stu>
<stu ID="a111">
<name>B</name>
<sex>male</sex>
<height>172</height>
</stu>-->

<ul id="a110">
<li>name:A</li>
<li>sex:male</li>
<li>height:175</li>
</ul>

<ul id="a111">
<li>name:B</li>
<li>sex:male</li>
<li>height:172</li>
</ul>
</student>